tests: add tests for missing revlogs and revlog entries The verify code is pretty poorly tested. It's easy to test missing revlogs and missing revlog entries, so let's add tests for that. Also add some more tests corrupting each type of revlog, so we test the messages presented when reading a revision fails. The pure and native implementations produce different error messages, so we have to use (glob) in the tests.

hook: don't crash on syntax errors in python hooks We had some real-world cases where syntax errors in Python hooks would crash the whole process and leave it in an indeterminate state. Handle those better.